The development of the laser and related light stimulative technology has generated a significant interest on the pan of investigators in that branch of interferometry known as "holography". In its underlying concept, holography generally considers that the scattering pattern of light from an object is a transform, or coded record, of the features of that object. Where such a scattering pattern is stored, for example, photographically, an image of the object should be reconstructable. Prior to the availability of an intense coherent light source, a required recordation of such patterns proved most difficult. However, with the availability of the laser as an intense coherent light source and with an innovation wherein the scattering pattern was combined to interfere with a reference beam of coherent light, a photographic wave-front reconstruction was realized. With the interference of reference and reflective subject beams, resultant interference fringes exhibit a recordable contrast representing a measure of amplitude of the subject beam and the position of these fringes represented a recordable measure of phase of the subject beam. Where a photograph of such interference pattern is illuminated with a laser beam identical with the original reference beam, deffracted light from the photograph will have the same amplitude and phase characteristics as the original beam from the subject.
The most interesting aspect of the holographic reconstruction resides in the very detailed and three-dimensional nature of the resultant image. These reconstructions, now referred to as "holograms" have found a variety of uses in commerce and the arts, however, their full potential in evoking three-dimensional images of objects has eluded investigators for many years.
Generally, holographic film technology mandates the vibration free environment of the optical bench or table, a stable platform the size of which is limited by practical constraints. In early holography, this size limitation, as well as the sizing of practical lens components, posed a limitation on the size of the scene being imaged. For example, a building or automobile could not be imaged in a vibration free environment which could only be achieved with an optical bench. Further compounding these imaging difficulties was the necessity for conventional film holography, in achieving appropriate parallax imaging, of deriving an aperture or film plate of dimensions wider and taller than the object being imaged. Confronted with these requirements, investigators turned to the synthetic aperture or synthetic window where imaged samplings, i.e. 35 mm black and white photographic transparencies, of a large object such as a building were made at spaced lateral intervals and radii from a front surface of the object. The samples or photographic slides then were returned to the optical table and imaged with a reference beam onto a holographic plate. This reference beam was angularly located in correspondence with the original angle of the slide to the scene at the time the photograph was made. A similar set-up and exposure ensued for the remaining slides or samples. The resultant holographic plate, when developed and illuminated with a single reference beam, reproduced the images of all the samples in an appropriate spatial disposition to achieve a three-dimensional visualization of the image as seen to a viewer. In this regard, as the viewer moved slightly laterally at the image plane, the eyes, through parallax, synthesize the scene from the different physical perspective as originally generated with the slide photography.
The substantial accuracy or fidelity evolved with film holography also led to the use of holographic recordings as a substitute for actual optical components of an optical system. In many cases, such optical components as now present within a holographic plate become more effective, with respect to utility, than their corresponding more conventional glass optics. This generation of holographic film optics also was enhanced with the generation of thicker emulsions and the like permitting the utilization of a large number of multiple exposures upon a single holographic plate, for example, as may be provided on plates of dichromated gelatin. In particular, advantage has been taken of the capability for recording several optical elements on a single, lightweight holographic glass film plate to achieve very wide field of view lens results which would otherwise be difficult to construct out of classic lens techniques. Leith, in the 1960's developed a highly useful technique for forming improved Fresnel zone plates for improved imaging quality over a wide field of view. See in this regard, U.S. Pat. No. 3,586,412 entitled "Holographic Lens with Aberration Correction" by Leith, issued Jun. 22, 1971.
Other investigators have turned their attention to what has been termed "real time" holography where a spatial light modulator is electronically driven to achieve an electronic reconstruction and display of a three-dimensional holographic image. Through resort to highly miniaturized grid matrix technology, the fringe pattern itself is constructed electrooptically. Such technology is, for example, described in U.S. Pat. No. 4,484,219 by Kirk, entitled "Electronically Generated Holography", issued Nov. 20. 1984. Improvements to the spatial modulator component of this technology described in U.S. Pat. No. 4,566,031 by Kirk, entitled "Spatial Light Modulation with Application to Electronically Generated Holography", issued Jan. 21, 1986.
A somewhat broad range of commercial entities have shown an interest in some form of practical 3-D presentation of objects. This interest has been enhanced by advances in computer graphics, where investigators have achieved refined levels of 2-D imaging including the computer generation of rotatable perspective views, a feature sometimes referred to as 21/2-D display. The value of such displays, particularly as generated in three dimensions, can be compared to the three-dimensional value of a partially completed sculpture to the sculpting artist. As a work of art gradually is formed, the artist, in effect, has the advantage of a continuous three-dimensional image of the work as it progresses to a final product such as a statue. Such 3-D information is far superior to the artist than a two-dimensional representation or a 21/2-D representation. These three-dimensional feedback needs easily extend from art to industry where the design of an article of manufacture such as an automobile or pan therefor, airplanes, and the like including architectural renderings typically are modeled to achieve a three-dimensional representation before final design is evolved. Three-dimensional holography, for example united with the improvements in computer graphics, holds promise to greatly enhance the capabilities of the industrial design artist.